1. Field of the Invention
The present invention relates to a device for securing an optical element, such as a beam splitter, installed in an optical pick-up device and, more particularly, to a device for securing an optical element to a securing section in an optical pick-up device with high precision.
2. Description of the Related Art
FIG. 4 schematically illustrates the internal structure of a conventional optical pick-up device. FIG. 5 is a sectional view of the inside of a base (i.e., a carriage) in which the conventional optical element is secured.
Referring to these figures, the conventional optical pick-up device comprises a laser diode 1 which emits a laser beam, an optical element 2, a reflecting mirror 3, an objective lens 4, and a light detector 5. These component parts are installed on a base (not shown) of the optical pick-up device in the positional relationship shown in FIG. 4. The laser beam irradiated from the laser diode 1 is incident on a side surface (that is, an incident surface) 2a of the optical element 2 at a predetermined angle of incidence. The optical element 2 may be, for example, a polarization beam splitter or a half mirror which can divide the incident light beam into two types of light beams, (i.e., a reflected light beam and a transmitted light beam). A portion of the light beam is reflected by the side surface 2a of the optical element 2 towards the reflecting mirror 3. The objective lens 4 is disposed above the reflecting mirror 3. The reflecting mirror 3 is inclined by a predetermined angle in the optical pick-up device in order to guide the reflected laser beam to the objective lens 4. A disk (not shown), such as a compact disk (CD) or a digital video disk (DVD), is mounted above the objective lens 4. By way of example, a focus-servo function (not illustrated) can be employed so that the objective lens 4 is capable of focusing the light beam reflected by the reflecting mirror 3 onto a signal-recording surface of the disk.
The returning light beam reflected from the signal-recording surface of the disk travels back to the optical element 2 by passing through the same path taken to reach the objective lens 4 in the opposite direction. Some of the returning light beam passes through the optical element 2, and is guided to the light detector 5 disposed behind the optical element 2. The light detector 5 may be, for example, a pin photodiode that detects the returning light beam that has passed through the optical element 2 in order to perform various signal processing operations thereon.
In the above-described optical pick-up device, the side surface 2a of the optical element 2 is an incident surface of the light beam from the laser diode 1 and a reflection surface which directs the light beam to the objective lens 4. Therefore, any tilting of the side surface 2a of the optical element 2 will effect, for example, the reading operation of the signal from the disk.
Therefore, when the optical element 2 is not precisely positioned at a predetermined location in the base of the optical pick-up device (i.e., when the side surface 2a is not oriented with high precision in a direction al where the laser diode 1 is disposed and in a direction b1 where the reflecting mirror 3 is disposed), then the center of the laser beam may get shifted from an optical axis O1 of the objective lens 4. This may cause aberrations to increase such that, for example, the shape of the laser beam spot formed on the signal-recording surface of the disk is distorted.
When the optical element 2 shifts in position or gets tilted, an optical axis O2 which extends to the light detector 5 gets shifted, resulting in problems such as the occurrence of offsetting in the focus-servo operation of the objective lens 4.
Conventionally, an attempt has been made to overcome this problem by, as shown in FIG. 5, forming a recess-shaped securing section 7 in a portion of a base 6, and securing the optical element 2 in the securing section 7. More specifically, conventional attempts have been made to overcome this problem by forming a bottom surface 7a of the securing section 7 parallel to a bottom surface 6a of the base 6, and by forming a mounting surface (i.e., a reference surface) 7b of the securing section 7 with high precision at an angle of 90 degrees from the bottom surface 7a of the securing section 7, or the bottom surface 6a of the base 6, in order to secure a portion of a surface of the optical element 2 to the mounting surface 7b in intimate contact therewith.
However, the base 6 is formed by die-casting a metal, such as aluminum or magnesium. Thus, the mold that is used to die-cast the metal must be removed from the base 6 in a direction perpendicular to the bottom surface 6a of the base 6 (i.e., in a direction parallel to the mounting surface 7b). When the mounting surface 7b is parallel to the direction in which the mold is removed, the mounting surface 7b and the mold rub against each other when the mold is removed, resulting in problems such as scratching and distortion of the mounting surface 7b. 
Therefore, conventionally, it has been necessary to provide excess metal (that is, machining allowance) with a small thickness on the mounting surface 7b, and to finish the mounting surface 7b with high precision by mechanically cutting the excess metal (i.e., the machining allowance) after removing the mold from the base 6. This complicates the manufacturing process of the base 6, resulting in increased manufacturing costs.
To overcome the above-described conventional problem, it is an object of the present invention to provide a device for securing an optical element capable of preventing rubbing occurring as a result of mold releasing, and allowing a surface for positioning the optical element with high precision to be formed when a molding operation is completed.
To this end, according to the present invention, there is provided a device for securing an optical element, in which a base includes a mounting surface formed substantially perpendicular to a surface of the base, and an optical element with a reference optical surface serving as a light-reflecting surface, a light-incident surface, or a light-exiting surface is positioned by bringing the reference optical surface and the mounting surface into intimate contact with each other, wherein:
the mounting surface is formed at an angle of 90 degrees plus a very small angle xcex81 with respect to the surface of the base.
The very small angle xcex81 may be greater than 0 degrees and equal to or less than 3 degrees.
In the present invention, by forming the mounting surface in the securing section of the base into an inclined surface, during removal of the base from the mold, the mounting surface of the base and the inclined molding surface of the mold can be properly separated from each other, so that, when a molding operation is completed, the mounting surface can be formed smoothly with high precision. Therefore, the mounting surface in a molded state can serve as a reference surface for securing the optical element, making it unnecessary to perform a mechanical cutting operation on the mounting surface after the removal of the base from the mold.
By providing a device for securing an optical element, in which a base includes a mounting surface formed substantially perpendicular to a surface of the base, and an optical element with a reference optical surface serving as a light-reflecting surface, a light-incident surface, or a light-exiting surface is positioned by bringing the reference optical surface and the mounting surface into intimate contact with each other, and in which the mounting surface is formed at an angle of 90 degrees plus a very small angle xcex81 with respect to the surface of the base, the base may include a bottom portion mounting surface formed at right angles to the mounting surface, the optical element may include a bottom surface formed at right angles to the reference optical surface, and the optical element may be positioned by bringing the reference optical surface into intimate contact with the mounting surface and by abutting the bottom surface against the bottom portion mounting surface.
By maintaining the mounting surface and the bottom portion mounting surface at right angles to each other, the optical element can be secured to the mounting surface with high precision. In other words, since the bottom surface and the reference optical surface of the optical element can be formed at right angles to each other with high precision, even if the mounting surface is inclined, the optical element can be secured in the securing section with high precision by setting the angle between the mounting surface and the bottom surface of the securing section at 90 degrees.
By providing a device for securing an optical element in which a base includes a mounting surface formed substantially perpendicular to a surface of the base, and an optical element with a reference optical surface serving as a light-reflecting surface, a light-incident surface, or a light-exiting surface is positioned by bringing the reference optical surface and the mounting surface into intimate contact with each other, and in which the mounting surface is formed at an angle of 90 degrees plus a very small angle xcex81 with respect to the surface of the base, the optical element may be supported in a cantilever manner by bringing one end of the reference optical surface extending in a widthwise direction along the surface of the base into intimate contact with the mounting surface, while an optical axis crossing an area of the reference optical surface is not brought into intimate contact with the mounting surface.
In this structure, by holding only one end of the optical element in a cantilever manner when the optical element is being secured, the other end can serve as a free end. Thus, this structure can prevent problems produced when both ends of the optical element are secured, such as dimensional differences between the mounting surfaces to which both ends of the optical element are secured. Therefore, the problem of the optical element becoming deformed when both ends of the reference optical surface of the optical element are forcibly secured to the mounting surfaces due to the dimensional differences between the mounting surfaces can be prevented from occurring. Consequently, it is possible to orient with high precision the optical axis which crosses (or is incident on, is reflected by, or passes through) the reference optical surface (i.e., the incident surface) of the optical element.
By providing a device for securing an optical element, in which a base includes a mounting surface formed substantially perpendicular to a surface of the base, and an optical element with a reference optical surface serving as a light-reflecting surface, a light-incident surface, or a light-exiting surface is positioned by bringing the reference optical surface and the mounting surface into intimate contact with each other, and in which the mounting surface is formed at an angle of 90 degrees plus a very small angle xcex81 with respect to the surface of the base, the base may be molded of a metallic material, and the mounting surface may be mechanically processed.